This invention relates generally to radio frequency lenses and more particularly to parallel plate radio frequency lenses.
As is known in the art, parallel plate radio frequency lenses, such as the type described in U.S. Pat. No. 3,761,936 entitled "Multi-beam Array Antenna," inventors Donald H. Archer, Robert J. Prickett and Curtis P. Hartwig, issued Sept. 25, 1973, and assigned to the same assignee as the present invention, have been used in a wide variety of applications. One such application is described in U.S. Pat. No. 3,715,749, inventor Donald H. Archer, issued Feb. 6, 1973, and assigned to the same assignee as the present invention. As described therein, such parallel plate lens has a plurality of "array" ports which are coupled to an array of antenna elements and a plurality of "beam" ports, each one of which is associated with a corresponding beam of radio frequency energy. The "array" ports and the "beam" ports are disposed about the periphery of the lens. In some applications, the shape of the lens may be substantially elliptical, in which case the "array" ports and the "beam" ports are disposed about opposite, or "facing," portions of the periphery of the lens. In such applications, radiation from each of the "beam" ports, during transmit, illuminates all of the "array" ports. However, in some applications it is necessary that the parallel plate lens be substantially circular in shape with the "array" ports disposed about half the circumference of the lens periphery and the "beam" ports being disposed about the remaining half of the circumference of the lens periphery. While efficient illumination is obtained with the central "beam" ports, the end "beam" ports may not provide adequate illumination of the "array" ports which are adjacent the excited end "beam" ports, thereby reducing the overall effectiveness of the lens. One technique suggested to improve the illumination effectiveness of the end "beam" ports has been to tie pairs of the end "beam" ports together through a power divider and cables of different electrical lengths to, in effect, steer the radiation towards the "array" port portion of the lens periphery. While such technique may be used effectively in some applications, it does not lend itself readily to printed circuit manufacturing techniques.